Dispersion behavior, surfactants

Although more work is needed to clearly correlate the type of solubilization site occupied by different porphyrins with their reactivity in such sites towards atropisomerization, it is clear that different sites exist and that these sites show quite different reactivity in both thermal and photochemical processes. Preliminary studies have shown that related behavior probably occurs in other organized assemblies formed by dispersion of surfactant molecules in... 

In the preceding section, we emphasized that the surface interaction of metallic particles with liquid molecules is a very important parameter in the dispersion behavior of the sol. Since the surface nature is very sensitive to the surface modification, we can easily regulate it with the use of surfactant. As seen in Figure 9.4.23, almost all metallic particles cannot be dispersed in hexane as a suspension liquid. In this section, we show what kind of surfactant is effective in dispersion. The sample was prepared by the gas flow-cold trap method. We tested three surfactants, dimethyldi-... 

Fouconnier, B., Avendano-Gomez, J., Ballerat, K., and Clausse, D. Effects of cooling-heating cycles on emulsions. Thermal Behavior of Dispersed Systems, Surfactant Science Series, Vol. 93, N. Garti, ed., Marcel Dekker, New York, 2000, chap. 5. 

The first four chapters thus provide a general background on interfacial phenomena, colloidal dispersions, and surfactants, with emphasis on their equilibrium properties. The remaining chapters deal with the dynamic behavior of interfaces, emphasizing this subject to a much greater degree than most books on interfacial phenomena. 

Garti, N., ed.. Thermal Behavior of Dispersed Systems, Surfactant Science Series Vol. 93, Marcel Dekker, New York, 2000. 

The WAG process has been used extensively in the field, particularly in supercritical CO2 injection, with considerable success (22,157,158). However, a method to further reduce the viscosity of injected gas or supercritical fluid is desired. One means of increasing the viscosity of CO2 is through the use of supercritical C02-soluble polymers and other additives (159). The use of surfactants to form low mobihty foams or supercritical CO2 dispersions within the formation has received more attention (160—162). Foam has also been used to reduce mobihty of hydrocarbon gases and nitrogen. The behavior of foam in porous media has been the subject of extensive study (4). X-ray computerized tomographic analysis of core floods indicate that addition of 500 ppm of an alcohol ethoxyglycerylsulfonate increased volumetric sweep efficiency substantially over that obtained in a WAG process (156). 

The overall set of partial differential equations that can be considered as a mathematical characterization of the processing system of gas-liquid dispersions should include such environmental parameters as composition, temperature, and velocity, in addition to the equations of bubble-size and residence-time distributions that describe the dependence of bubble nucleation and growth on the bubble environmental factors. A simultaneous solution of this set of differential equations with the appropriate initial and boundary conditions is needed to evaluate the behavior of the system. Subject to the Curie principle, this set of equations should include the possibilities of coupling effects among the various fluxes involved. In dispersions, the possibilities of couplings between fluxes that differ from each other by an odd tensorial rank exist. (An example is the coupling effect between diffusion of surfactants and the hydrodynamics of bubble velocity as treated in Section III.) As yet no analytical solution of the complete set of equations has been found because of the mathematical difficulties involved. To simplify matters, the pertinent transfer equation is usually solved independently, with some simplifying assumptions. 

The cost/performance factor of individual surfactants will always be considered in determining which surfactants are blended in a mixed active formulation. However, with the recent advent of compact powders and concentrated liquids, other factors, such as processing, density, powder flowability, water content, stabilization of additives, dispersibility in nonaqueous solvents, dispersion of builders, and liquid crystalline phase behavior, have become important in determining the selection of individual surfactants. 

The effects of different surfactants on the rheological behavior of cement-water dispersions were studied by a rotational-type viscometer. The type of... 

Salts of alkyl phosphates and types of other surfactants used as emulsifiers and dispersing agents in polymer dispersions are discussed with respect to the preparation of polymer dispersions for use in the manufactoring and finishing of textiles. Seven examples are presented to demonstrate the significance of surfactants on the properties, e.g., sedimentation, wetting behavior, hydrophilic characteristics, foaming behavior, metal adhesion, and viscosity, of polymer dispersions used in the textile industry [239]. 

The preparation and study of metal nanoparticles constitutes an important area of current research. Such materials display fascinating chemical and physical properties due to their size [62, 63]. In order to prevent aggregation, metal nanoparticles are often synthesized in the presence of ligands, functionalized polymers and surfactants. In this regard, much effort has focused on the properties of nanoparticles dispersed into LCs. In contrast, the number of nanoparticles reported that display liquid crystal behavior themselves is low. Most of them are based on alkanethiolate stabilized gold nanoparticles. 

The performance of demulsifiers can be predicted by the relationship between the film pressure of the demulsifier and the normalized area and the solvent properties of the demulsifier [1632]. The surfactant activity of the demulsifier is dependent on the bulk phase behavior of the chemical when dispersed in the crude oil emulsions. This behavior can be monitored by determining the demulsifier pressure-area isotherms for adsorption at the crude oil-water interface. 

Disperse systems can also be classified on the basis of their aggregation behavior as molecular or micellar (association) systems. Molecular dispersions are composed of single macromolecules distributed uniformly within the medium, e.g., protein and polymer solutions. In micellar systems, the units of the dispersed phase consist of several molecules, which arrange themselves to form aggregates, such as surfactant micelles in aqueous solutions. 

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